The present invention relates to a wheel anti-skid brake control system adapted particularly for automotive type vehicles, such as trucks for example, wherein there is provided separate wheel anti-skid brake control channels for each axle.
In addition to the usual wheel behavior sensing and evaluation circuitry, modulator valve means and power supply unit, each control channel may further include a safety circuit capable of detecting operating malfunctions arising in critical portions of the control channel in order to prevent inadvertent control signals from adversely influencing the anti-skid control system operation. These safety circuits are well-known, being operative responsively to the mentioned inadvertent control signals to cut off the power supply unit from each control channel and thereby interrupt influence of the anti-skid control system on the fluid brake pressure, as controlled by the vehicle operator via the main brake valve device.
Recent technological developments in the field of electronics have reached the point where integrated circuitry is now feasible in the design of an electronic wheel anti-skid brake control system of the above type. In employing integrated circuit design, the control system is no longer able to be separated into individual control circuits for the different control functions performed, since as many circuit functions as possible are concentrated into each integrated circuit chip. For this reason, the possibility exists that the safety circuit of a given control channel may be rendered inoperative in the event a malfunction arises in the integrated circuit of which the safety circuit is a part. Being inoperative, the safety circuit will of course fail to detect a subsequent malfunction for which it is designed to detect and which most likely would arise as a result of the malfunction existing in the integrated circuit. Failure of the safety circuit to monitor malfunctions of the wheel anti-skid control system, of course, results in the possibility of the wheel anti-skid control system exerting an adverse influence upon the wheel brake pressure without the operator being aware of this potentially dangerous situation.